Self-Concentrating Absorbent for Acid Gas Separation

ABSTRACT

A process and systems for efficiently deacidizing a gaseous mixture is described. The process and systems utilize a self-concentrating absorbent that absorbs an acid gas at reduced overall energy costs for the deacidizing operation.

REFERENCE TO RELATED APPLICATIONS

This application is a division of Application U.S. patent applicationSer. No. 12/430,998 filed Apr. 28, 2009, published Oct. 22, 2009 as U.S.patent publication No. 20090263302 A1, which is a continuation-in-partpatent application of U.S. patent application Ser. No. 12/250,257, filedon Oct. 13, 2008, issued as U.S. Pat. No. 7,718,151 on May 18, 2010,titled “Methods and Systems For Deacidizing Gaseous Mixtures,” which isa continuation-in-part patent application of U.S. patent applicationSer. No. 11/279,095, filed on Apr. 7, 2006, issued as U.S. Pat. No.7,541,011 on Jun. 2, 2009, titled “Phase Transitional AbsorptionMethod,” all of which are hereby incorporated by reference herein intheir entirety.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of NationalScience Foundation SBIR Award No. IIP-0839217.

FIELD OF THE INVENTION

The present invention relates to a process for deacidizing a gaseousmixture using a self-concentrating absorbent. More particularly, thepresent invention relates to a method for the separation of an acid gasfrom a gaseous mixture using a self-concentrating absorbent, whichreduces the overall energy costs for such deacidizing operation.

BACKGROUND OF THE INVENTION

Removal of acid gas from gas mixture is required for many processes,such as, deacidization of a raw natural gas or any other gaseous mixturethat contains significant amounts of an acid gas, e.g., hydrogen sulfide(H₂S), carbon dioxide (CO₂), or similar contaminants. The deacidizationprocess reduces the acid gas impurity in the gaseous mixture toacceptable levels. This is commonly done with an amine gas treatmentprocess. Amine gas treatment processes are common in various types ofindustrial settings, such as refineries, natural gas processing plants,and petrochemical plants. Amine gas treatment processes include theprocesses utilizing aqueous solutions of amines to remove acid gas, suchas H₂S and CO₂.

A common deacidization process is gas-liquid absorption. Such processtypically involves contacting a gaseous mixture containing an acid gasto be removed with an aqueous amine solution, whereby the amine solutionis an absorbent that absorbs the acid gas. In industrial settings, themost commonly used amines are alkanolamines, such as monoethanolamine(MEA) and diethanolamine (DEA). The use of the alkanolaminemethyldiethanolamine (MDEA) for CO₂ separation has recently becomenotable for use in industrial settings. Diisopropanolamine (DIPA) iscurrently used in the Sulfinol process and in the SCOT process for Clausplant tail acid gas purification.

In the typical gas-liquid absorption process, after an acid gas isabsorbed into the absorbent in an absorption unit, the gas-richabsorbent is sent to a regeneration unit, where the gas-rich absorbentis treated and separated to regenerate the absorbed gas and the gas-leanabsorbent. The regenerated gas-lean absorbent is then recycled back intothe absorption unit and the acid gas is either collected or discharged,depending on the purpose of the user. In this type of gas-liquidabsorption, the regeneration process accounts for greater than 80% ofthe total energy costs because the entire volume of the absorbenteffluent must be regenerated in order to be reused in the absorptionunit. In addition, the typical gas-liquid absorption process is limitedto the use of an absorbent in the form of one liquid phase.

BRIEF SUMMARY OF THE INVENTION

It is now discovered that a method for deacidizing a gaseous mixtureinvolving a self-concentrating absorbent increases the absorption rateof an acid gas from the gaseous mixture and reduces the overall energycosts for such deacidizing operation.

In one general aspect, embodiments of the present invention relate to amethod for deacidizing a gaseous mixture comprising an acid gas. Themethod comprises:

contacting the gaseous mixture with an absorbent in an absorption unit,wherein the absorbent comprises an amine dissolved in a solvent at afirst concentration;

allowing the absorbent to absorb the acid gas to form aconcentrated-amine phase, wherein the concentrated-amine phase ismechanically separable from the remaining of the absorbent and comprisesa concentrated amine at a concentration higher than the firstconcentration and an absorbed acid gas, wherein the concentrated aminecomprises the amine or the amine having a chemical modification, and theabsorbed acid gas comprises the acid gas or the acid gas having achemical modification;

separating the concentrated-amine phase from the remaining of theabsorbent;

cycling the remaining of the absorbent back into the absorption unit;

providing the concentrated-amine phase to a regeneration unit, so as toobtain the acid gas and the concentrated amine; and

cycling the regenerated concentrated amine back into the absorptionunit.

In an embodiment of the present invention, the absorbent and theabsorbed acid gas move downward from the absorption unit to theseparation unit by gravity, and the separated concentrated-amine phasemoves downward from the separation unit to the regeneration unit bygravity.

In another general aspect, embodiments of the present invention relateto a system for deacidizing a gaseous mixture comprising an acid gas.The system comprises:

an absorption unit adapted to allow contact between the gaseous mixtureand an absorbent comprising an amine dissolved in a solvent at a firstconcentration, wherein the absorbent absorbs the acid gas to form aconcentrated-amine phase, wherein the concentrated-amine phase ismechanically separable from the remaining of the absorbent, and theconcentrated-amine phase comprises a concentrated amine at aconcentration higher than the first concentration and an absorbed acidgas, wherein the concentrated amine comprises the amine or the aminehaving a chemical modification, and the absorbed acid gas comprises theacid gas or the acid gas having a chemical modification

a separation unit adapted to allow separation of the concentrated-aminephase from the remaining of the absorbent; and

a regeneration unit adapted to allow regeneration of theconcentrated-amine phase, so as to obtain the acid gas and theconcentrated amine.

In an embodiment of the present invention, the absorption unit, theseparation unit and the regeneration unit are in a single tower, whereinthe separation unit is placed in a position lower than the absorptionunit and the regeneration unit is placed in a position lower than theseparation unit, so that after the gas absorption, the absorbent and theabsorbed acid gas move downward from the absorption unit to theseparation unit by gravity, and the concentrated-amine phase movesdownward from the separation unit to the regeneration unit by gravity.

In yet another general aspect, embodiments of the present inventionrelate to a method for deacidizing a gaseous mixture comprising an acidgas. The method comprises:

contacting the gaseous mixture with an absorbent in an absorption unit,wherein the absorbent comprises an agent dissolved in a solvent at afirst concentration, wherein the agent is selected from the groupconsisting of amino-acid salts, amides, alkaline salts, alkaline-earthsalts, ammonium salts, ureas, alkaline metal phosphates, carbonates,borates, acid phosphites, phosphites, phosphonite, phosphinate,phosphonate, acid phosphates, pyrophosphites, bicarbonates, metaborates,diborates, tetraborates, pentaborates, and combinations thereof;

allowing the absorbent to absorb the acid gas to form aconcentrated-agent phase, wherein the concentrated-agent phase ismechanically separable from the remaining of the absorbent and comprisesa concentrated agent at a concentration higher than the firstconcentration and an absorbed acid gas, wherein the concentrated agentcomprises the agent or the agent having a chemical modification, and theabsorbed acid gas comprises the acid gas or the acid gas having achemical modification;

separating the concentrated-agent phase from the remaining of theabsorbent;

cycling the remaining of the absorbent back into the absorption unit;

providing the concentrated-agent phase to a regeneration unit, so as toobtain the acid gas and the concentrated agent; and

cycling the regenerated concentrated agent back into the absorptionunit.

In another general aspect, embodiments of the present invention relateto a system for deacidizing a gaseous mixture comprising an acid gas.The system comprises:

an absorption unit adapted to allow contact between the gaseous mixtureand an absorbent comprising an agent dissolved in a solvent at a firstconcentration,

-   -   wherein the agent is selected from the group consisting of        amino-acid salts, amides, alkaline salts, alkaline-earth salts,        ammonium salts, ureas, alkaline metal phosphates, carbonates,        borates, acid phosphites, phosphites, phosphonite, phosphinate,        phosphonate, acid phosphates, pyrophosphites, bicarbonates,        metaborates, diborates, tetraborates, pentaborates, and        combinations thereof;    -   wherein the absorbent absorbs the acid gas to form a        concentrated-agent phase, the concentrated-agent phase is        mechanically separable from the remaining of the absorbent, and        the concentrated-agent phase comprises a concentrated agent at a        concentration higher than the first concentration and an        absorbed acid gas,    -   wherein the concentrated agent comprises the agent or the agent        having a chemical modification, and the absorbed acid gas        comprises the acid gas or the acid gas having a chemical        modification;

a separation unit adapted to allow separation of the concentrated-agentphase from the remaining of the absorbent; and

a regeneration unit adapted to allow regeneration of theconcentrated-agent phase, so as to obtain the acid gas and theconcentrated agent.

Other aspects, features and advantages of the invention will be apparentfrom the following disclosure, including the detailed description of theinvention and its preferred embodiments and the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown.

In the drawings:

FIG. 1 is a flow diagram showing the steps of the deacidization processaccording to an embodiment of the present invention; and

FIG. 2 is a flow diagram showing the steps of the deacidization processaccording to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this invention pertains. Otherwise, certain terms usedherein have the meanings as set in the specification. All patents,published patent applications and publications cited herein areincorporated by reference as if set forth fully herein. It must be notedthat as used herein and in the appended claims, the singular forms “a,”“an,” and “the” include plural reference unless the context clearlydictates otherwise.

In one general aspect, the present invention relates to a process ofdeacidizing a gaseous mixture using a self-concentrating amineabsorption, while minimizing energy costs and maximizing absorptionrates.

According to an embodiment of the present invention, an absorbent and agaseous mixture containing an acid gas to be removed are contacted in anabsorption unit. The absorbent comprises an amine or an agent dissolvedin a solution at a first concentration. During the absorption, amine orthe agent in the absorbent is spontaneously concentrated into aconcentrated-amine or concentrated-agent phase. After the absorption iscomplete, the concentrated-amine or concentrated-agent phase ismechanically separable from the remaining of the absorbent, i.e., theconcentrated-amine or concentrated-agent phase does not form a solutionwith the remaining of the absorbent.

The acid gas to be removed can be, for example, one or more acid gasesselected from the group consisting of carbon dioxide (CO₂), sulfurdioxide (SO₂), sulfur trioxide (SO₃), hydrogen sulfide (H₂S), carbonoxysulfide (COS), carbon disulfide (CS₂), mercaptans (RSH), nitric oxide(NO), nitric dioxide (NO₂), fluorides, HCl, and a combination thereof.

The absorption unit according to embodiments of the present inventioncan be, for example, an absorption column or a membrane contractor, orany other gas-liquid contacting units that are known to those skilled inthe art.

It is readily appreciated by those skilled in the art that the absorbentcan comprise one or more amines dissolved in a solvent. Examples of theamines include, but are not limited to monoethanolamine, diethanolamine,triethanolamine, ethanolamines, isopropanolamines, ethyleneamines, alkylalkanolamines, methyldiethanolamine, piperidine, dibutylamine,diisopropylamine, derivatives thereof, or mixtures thereof.

The solvent can be aqueous or organic. For example, the aqueous solventcan be water, an aqueous solution of one or more salts, including, butnot limited to, alkaline salts, ammonium salts, alkanolamine salts,alkaline-earth salts, or derivatives thereof. The organic solvent cancomprise one or more components, including, but not limited to,alcohols, glycols, alkanes, unsaturated hydrocarbon, ethers, esters,aldehyde, ketones, glycol ethers, alkylene carbonates, dialkylcarbonates, sulfolane, and derivatives thereof, such as ionic liquids,polymers. The solvent can further be a combination of an aqueoussolution and an organic solvent.

In a preferred embodiment, the organic solvent comprises a C₈ to C₁₂alcohol.

The solvent can also be water insoluble or slightly water solublesolvent, such as water insoluble alcohol, glycol, or glycol ether. Thesolvent can further be ionic liquids or polymers.

In an embodiment of the present invention, the absorbent comprises anamine solution, including, but not limited to an alcohol, glycol orglycol ether solution of monoethanolamine, diethanolamine,triethanolamine, ethanolamines, isopropanolamines, ethyleneamines, alkylalkanolamines, methyldiethanolamine, piperidine, dibutylamine,diisopropylamine, derivatives thereof, or mixtures thereof.

In an embodiment of the present invention, the amine can be anotheragent instead, the other agent can be amino-acids, amino-acid salts,amides, alkaline salts, ammonium salts, ureas, alkaline metalphosphates, carbonates, borates, acid phosphites, phosphites,phosphonite, phosphinate, phosphonate, acid phosphates, pyrophosphites,bicarbonates, metaborates, diborates, tetraborates, pentaborates,derivatives thereof, or combinations thereof. The solvent can be water,an aqueous solution of one or more salts, including, but not limited to,alkaline salts, ammonium salts, alkanolamine salts, alkaline-earthsalts, ureas, alkaline metal phosphates, acid phosphites, phosphites,phosphonite, phosphinate, phosphonate, acid phosphates, pyrophosphites,carbonates, bicarbonates, borates, metaborates, diborates, tetraborates,pentaborates, or derivatives thereof. The organic solvent can compriseone or more components, including, but not limited to, alcohols,glycols, alkanes, unsaturated hydrocarbon, ethers, esters, aldehyde,ketones, glycol ethers, alkylene carbonates, dialkyl carbonates,sulfolane, and derivatives thereof, such as ionic liquids, polymers,such as, the absorbent comprises a carbonates or borates aqueoussolution.

In an embodiment of the present application, the absorbent comprises asolution of an amine at a concentration selected from the groupconsisting of 0.1%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%,55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.

According to embodiments of the present invention, when the acid gascontacts with the absorbent, the acid gas can be absorbed physically,chemically, or both physically and chemically. After physicalabsorption, the acid gas is absorbed in the absorbent, mainly in theconcentrated-amine phase, without being chemically modified. Afterchemical absorption, however, the acid gas is absorbed in the absorbent,mainly in the concentrated-amine phase, after being chemically modified,e.g., in a reaction product of the amine and the acid gas.

In one embodiment of the present invention, the reaction product of theamine with the acid gas is substantially insoluble in the solvent.

The concentrated-amine phase comprises a concentrated amine at aconcentration higher than the first concentration and an absorbed acidgas. The concentrated amine can be the amine or the amine having achemical modification, for example, a reaction product resulting from achemical reaction between the amine and the acid gas. The absorbed acidgas can be the acid gas or the acid gas having a chemical modification,for example, a reaction product resulting from a chemical reactionbetween the amine and the acid gas. The concentrated-amine phase canexist as a single phase, e.g., a solution of amine. Theconcentrated-amine phase can also contain multiple phases.

Because the absorbent forms the concentrated-amine phase spontaneouslyupon absorption of the acid gas, the absorbent is also referred to asthe self-concentrating amine absorbent.

The absorbed acid gas accumulates in the concentrated-amine phase.

After the absorbent absorbs the acid gas, the purified gaseous mixture,with the acid gas being removed or significantly reduced, is releasedfrom the absorption unit. The released purified gaseous mixture can becollected or disposed of, depending on the user's purpose.

After the absorbent absorbs the acid gas, the contents of the absorptionunit are provided to a separation unit to separate theconcentrated-amine phase from the remaining of the absorbent. Theformation of the concentrated-amine phase can proceed before,simultaneously, or after the contents of the absorption unit areprovided to the separation unit.

In one embodiment of the present invention, the contents of theabsorption unit are provided to the separation unit after the completeformation of the concentrated-amine phase.

In another embodiment of the present invention, the contents of theabsorption unit are provided to the separation unit before the completeformation of the concentrated-amine phase.

The separation can be achieved using phase separation methods known tothose skilled in the art in view of the present disclosure. For example,the concentrated-amine phase can be separated based on the density ofthe phase, e.g., by a separating drum. The concentrated-amine phase canalso be separated based on other properties of the phase, e.g., by amembrane that has different permeability to the concentrated-amine phaseand the remaining of the absorbent.

The separating step of the present invention can be accomplishedutilizing one or more types of phase settlers or phase separation unitsknown in the art as suited for separation of bulk liquid phases. Someexamples include simple settlers, filtration, centrifugation, membrane,etc.

After the separation, the remaining of the absorbent contains mostly thesolvent. It can also contain the amine at a concentration much lowerthan the first concentration. The remaining of the absorbent can furthercontain a small amount of the absorbed acid gas. After the separation,the remaining of the absorbent is cycled back into the absorption unitfor reuse.

The separated concentrated-amine phase is routed to a regeneration unit,where the concentrated-amine phase is treated to produce or regeneratethe amine and the acid gas. The regeneration process according toembodiments of the present invention can be accomplished by regenerationmethods known to those skilled in the art in view of the presentdisclosure. Exemplary regeneration methods include, but are not limitedto, thermal decomposition, gas stripping, steam stripping, distillation,treatment through a membrane contractor, pervaporization, pressuredifferential treatment, and a combination thereof.

The regenerated acid gas is collected or disposed of depending on thepurpose of the user. The regenerated amine is cycled back into theabsorption unit for reuse.

In an embodiment of the present invention, the contents of the absorbentare transferred from one unit to another unit by a pump. In otherembodiments of the present invention, the contents of the absorbent aretransferred between at least some of the units by gravity.

In an embodiment of the present invention, the contents of the absorbentmove downward from the absorption unit to the separation unit bygravity.

In another embodiment of the present invention, the separatedconcentrated-amine phase moves downward from the separation unit to theregeneration unit by gravity.

In still another embodiment of the present invention, the contents ofthe absorbent move downward from the absorption unit to the separationunit, and the separated concentrated-amine phase moves downward from theseparation unit to the regeneration unit, all by gravity.

In another general aspect, the present invention relates to a system fordeacidizing a gaseous mixture comprising an acid gas. The systemcomprises an absorption unit, a separation unit and a regeneration unitas those described herein.

In an embodiment of the present invention, the separation unit is placedin a position lower than the absorption unit, so that the contents ofthe absorbent move downward from the absorption unit to the separationunit by gravity.

In another embodiment of the present invention, the regeneration unit isplaced in a position lower than the separation unit, so that theseparated concentrated-amine phase moves downward from the separationunit to the regeneration unit by gravity.

In still another embodiment of the present invention, the absorptionunit, the separation unit and the regeneration unit are placed in asingle tower, wherein the separation unit is placed in a position lowerthan the absorption unit and the regeneration unit is placed in aposition lower than the separation unit, so that the gas-rich absorbentmoves downward from the absorption unit to the separation unit bygravity, and the separated concentrated-amine phase moves downward fromthe separation unit to the regeneration unit by gravity.

The deacidization process according to embodiments of the presentinvention can be used to remove an impurity acid gas from a gaseousmixture, in which case the impurity acid gas can be disposed of, withimproved efficiency. Alternatively, the deacidization process accordingto embodiments of the present invention can be used to collect an acidgas of interest from a gaseous mixture, with improved efficiency.

In one embodiment of the present invention, the solvent in an absorbentaccording to an embodiment of the present invention serves to increasethe absorption rate of the acid gas. The acid gas is absorbed into theabsorbent at a rate greater than that if it were directly absorbed bythe amine.

In an aspect of the present invention, the energy to be expended for theregeneration process is reduced because only part of the absorbent, theconcentrated-amine phase, needs to be regenerated, while the remainingof the absorbent can immediately be recycled for reuse in the absorptionunit.

In yet another aspect of the present invention, the energy to beexpended for the deacidization process is further reduced byincorporating two or more of the units used in the process in a singletower, so that the various components can be transferred between some ofthe units by gravity, instead of pumping. The use of multiple units in asingle tower is enabled and becomes practical, because of the relativelysmaller size of the concentrated-amine phase that needs to beregenerated. In a conventional liquid-gas separation process, the volumeof the gas-rich absorbent that needs to be regenerated is significantlylarger than that of the concentrated-amine phase according toembodiments of the present invention. Thus, in the conventional methods,a single tower containing the absorption unit and the regeneration unitwould be too tall to be practical.

FIG. 1 illustrates a particular embodiment of the present invention. Agaseous mixture 1 containing an acid gas to be removed and an absorbent3 are provided into an absorption unit 10. The gaseous mixture 1 and theabsorbent 3 contact with each other in the absorption unit 10. After theacid gas is absorbed in the absorbent 3 in the absorption unit 10, thepurified gaseous mixture 2 is released from the absorption unit 10. Thegas-rich absorbent 5 is sent to a separation unit 20, such as a gravitysettler tank, for separating the concentrated-amine phase 6 from theremaining of the absorbent 4. After the separation, the remaining of theabsorbent 4, comprising most or all components of the solvent and littleor none of the amine and little or none of the absorbed acid gas, iscycled back into the absorption unit 10 for reuse, with or withoutfurther treatment. The separated concentrated-amine phase 6, containingmost or all of the amine and the absorbed acid gas, both with or withoutchemical modification, optionally one or more components of the solvent,is provided for regeneration.

Referring to FIG. 1, the separated concentrated-amine phase 6 is routedto a regeneration unit 30, where the concentrated-amine phase 6 istreated to separate the absorbed acid gas 12 from the rest of theconcentrated-amine phase, which is the gas-lean phase 14. The absorbedacid gas 12 is further treated to separate the acid gas 18 from the rest16, which may contain the amine and one or more components of thesolvent that react with the acid gas during the absorption of the acidgas and/or the transfer of the absorbed acid gas. The separated acid gas18 can be disposed of or collected, depending on the user's purpose. Therest 16 is regenerated as part of the gas-lean phase 14. The gas-leanphase 14, which contains the regenerated amine and optionally one ormore components of the solvent, is cycled back into the absorption unit10 for reuse, with or without further treatment.

As shown in FIG. 1, the remaining of the absorbent 4 from the separationunit 20 and the gas-lean phase 14 from the regeneration unit 30 aremixed together in a mixer 40. The resulting absorbent 3 is then cycledback into the absorption unit 10 for reuse. According to otherembodiments of the present invention, the remaining of the absorbent 4and the gas-lean phase 14 can each be cycled back into the absorptionunit 10 for reuse without being first mixed together.

Although not shown in FIG. 1, in view of the present disclosure, it isreadily appreciated by those skilled in the art that, in addition to thecycled back components of the absorbent 3, additional one or morecomponents of the absorbent 3 can be added to compensate for the loss ofthe one or more components during the deacidizing process.

FIG. 2 illustrates another particular embodiment of the presentinvention. In this process, the absorption unit 10, separation unit 20and regeneration unit 30 are grouped inside a single tower 100. Thegas-rich absorbent from the absorption unit 10 flows downward into theseparation unit 20 by gravity, so as to separate the concentrated-aminephase and the remaining of the absorbent 4. After separation, theconcentrated-amine phase flows downward into the regeneration unit 30,by gravity, where the regenerated acid gas 18 and the gas-lean phase 14are obtained. The remaining of the absorbent 4 and the gas-lean phase 14further flow downward into the mixer 40, and are mixed in the mixer 40to obtain the absorbent 3. The absorbent 3 is pumped back into theabsorption unit 10, where it forms contact with the gaseous mixture 1,to start another cycle.

According to other embodiments of the present invention, the remainingof the absorbent 4 and the gas-lean phase 14 can each be pumped backinto the absorption unit 10 for reuse without being first mixedtogether.

Again, in addition to the cycled back components of the absorbent 3,additional one or more components of the absorbent 3 can be added tocompensate for the loss of the one or more components during thedeacidizing process.

In this embodiment, no pumping energy is required for liquid transferfrom the absorption unit 10 to the regeneration unit 30, thus achievesfurther energy saving.

The following examples illustrate the invention but are in no wayintended to limit the scope of the present invention.

Example 1

The absorbent was made of 20% by volume of the amine, monoethanolamine(MEA), and 80% by volume of the solvent, iso-octanol. The absorbent wascontacted with a gaseous mixture containing an acid gas, carbon dioxide(CO₂), in a stirring cell absorption unit at about 25-45° C., 1 atm. MEAin the absorbent was concentrated spontaneously into aconcentrated-amine phase, which contained MEA and the reaction productof MEA and CO₂.

After the absorption, the absorbent was settled to separate by gravitythe concentrated-amine phase from the remaining of the absorbent. Afterthe separation, the remaining of the absorbent, which contains most ofthe iso-octanol and optionally some MEA and absorbed CO₂, was cycledback into the absorption unit for reuse. In the concentrated-aminephase, the concentration of the total MEA, which includes the chemicallyunmodified MEA and the reaction product of MEA and CO₂, was about 70% byvolume.

The separated concentrated-amine phase was forwarded to a regeneratorand was treated to obtain the regenerated MEA and CO₂. by the method ofheating the concentrated-amine phase. The regenerated MEA was mixed withthe remaining of the absorbent. The mixture was cycled back to thestirring cell absorption unit to complete the cycle.

The CO₂ released from the regeneration process was collected.

Example 2

This example illustrates the absorption of CO₂ by a carbonate aqueoussolution.

An absorbent is made of carbonate aqueous solution. The absorbent iscontacted with a gas mixture containing acid gas, carbon dioxide (CO₂),in a stirring cell absorption unit at 50° C., 1 atm.

During the absorption, carbonate in aqueous solution reacts with CO₂ toform bicarbonate. After absorption, the absorbent is cooled to 25° C.and the bicarbonate is crystallized. The bicarbonate solid phase isseparated from the absorbent. It is then forwarded to a regenerationsection and is treated to obtain the regenerated carbonate and CO₂ bythe method of heating the solid phase of bicarbonate. The regeneratedcarbonate is dissolved in aqueous solution and cycled back to thestirring cell absorption unit to complete the cycle.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. A system for deacidizing a gaseous mixture comprising an acid gas,comprising: an absorption unit adapted to allow contact between thegaseous mixture and an absorbent comprising an amine dissolved in asolvent at a first concentration, wherein the absorbent absorbs the acidgas to form a concentrated-amine phase, wherein the concentrated-aminephase is mechanically separable from the remaining of the absorbent, andthe concentrated-amine phase comprises a concentrated amine at aconcentration higher than the first concentration and an absorbed acidgas, wherein the concentrated amine comprises the amine or the aminehaving a chemical modification, and the absorbed acid gas comprises theacid gas or the acid gas having a chemical modification a separationunit adapted to allow separation of the concentrated-amine phase fromthe remaining of the absorbent; and a regeneration unit adapted to allowregeneration of the concentrated-amine phase, so as to obtain the acidgas and the concentrated amine.
 2. The system of claim 1, wherein theseparation unit is placed in a position lower than the absorption unit,so that after the absorbent absorbs the acid gas to form a gas-richabsorbent, the gas-rich absorbent moves downward from the absorptionunit to the separation unit by gravity.
 3. The system of claim 2,wherein the absorption unit, the separation unit and the regenerationunit are placed in a single tower, wherein the separation unit is placedin a position lower than the absorption unit and the regeneration unitis placed in a position lower than the separation unit, so that afterthe absorbent absorbs the acid gas, the gas-rich absorbent movesdownward from the absorption unit to the separation unit by gravity, andafter the step of separation, the concentrated-amine phase movesdownward from the separation unit to the regeneration unit by gravity.4. The system of claim 1, wherein the regeneration unit is placed in aposition lower than the separation unit, so that after the step ofseparation, the concentrated-amine phase moves downward from theseparation unit to the regeneration unit by gravity.
 5. A system fordeacidizing a gaseous mixture comprising an acid gas, comprising: anabsorption unit adapted to allow contact between the gaseous mixture andan absorbent comprising an agent dissolved in a solvent at a firstconcentration, wherein the agent is selected from the group consistingof amino-acid salts, amides, alkaline salts, alkaline-earth salts,ammonium salts, ureas, alkaline metal phosphates, carbonates, borates,acid phosphites, phosphites, phosphonite, phosphinate, phosphonate, acidphosphates, pyrophosphites, bicarbonates, metaborates, diborates,tetraborates, pentaborates, and combinations thereof; wherein theabsorbent absorbs the acid gas to form a concentrated-agent phase, theconcentrated-agent phase is mechanically separable from the remaining ofthe absorbent, and the concentrated-agent phase comprises a concentratedagent at a concentration higher than the first concentration and anabsorbed acid gas, wherein the concentrated agent comprises the agent orthe agent having a chemical modification, and the absorbed acid gascomprises the acid gas or the acid gas having a chemical modification; aseparation unit adapted to allow separation of the concentrated-agentphase from the remaining of the absorbent; and a regeneration unitadapted to allow regeneration of the concentrated-agent phase, so as toobtain the acid gas and the concentrated agent.
 6. The system of claim5, wherein the solvent comprises water, an aqueous solution containingone or more salts selected from alkaline salts, ammonium salts,alkanolamine salts, alkaline-earth salts, phosphates, acid phosphites,phosphites, phosphonite, phosphinate, phosphonate, acid phosphates,pyrophosphites, carbonates, bicarbonates, borates, metaborates,diborates, tetraborates, or pentaborates.